Golf shafts are generally tapering, hollow tubes with a circular cross-section having a minimum outer diameter (OD) at an extreme, tip end where the shaft attaches to a club head and a maximum outer diameter at an opposite extreme, butt end around which a grip is applied. Typical minimum outer diameters range from 0.335″ to 0.400″. Typical maximum outer diameters range from 0.550″ to 0.650″. Golf shafts often include substantially cylindrical, parallel sections at the extreme ends to account for hosel (tip) and grip (butt) geometries, and to allow for trimming of the parallel sections (tip trimming to increase stiffness, butt trimming to adjust club length) while maintaining compatibility with hosel and grip. Typical OD taper rates between the extreme ends may vary, but generally range from 0.006 in/in to 0.014 in/in, with driver shaft profiles, for example having a taper of about 0.009-0.010 in/in in the section between the parallel tip and parallel butt.
Increasing a shaft's diameter in a given section is a primary design lever used to increase shaft stiffness without having to add mass or increase material modulus. Lighter shafts are generally beneficial to a golfer in order to reduce effort to swing the club and increase club head speed. Lower modulus materials are typically less expensive and more durable. These reasons drive shaft designs to generally larger diameters. However, aerodynamic drag is increased with larger diameter shafts due to the increased projected area along the path of the shaft in a swing.
Drag force is also proportional to the square of the air flow velocity across the shaft. Since the tip end of the shaft is moving the fastest in a golf swing, the tip end is a significant contributor to drag and reduces club head speed.
While this provided background description attempts to clearly explain certain club-related terminology, it is meant to be illustrative and not limiting. Custom within the industry, rules set by golf organizations such as the United States Golf Association (USGA) or The R&A, and naming convention may augment this description of terminology without departing from the scope of the present application.